1. Field of the Invention
This invention relates to novel polymeric materials and is more particularly concerned with polymeric materials in which the major recurring polymer unit is an isocyanurate moiety.
2. Description of the Prior Art
The trimerization of organic polyisocyanates to form polyisocyanurates useful in a number of applications such as binding agents, laminating or impregnating resins, adhesives, shaped articles, and the like, has been well known for some time to those skilled in the art; see for example U.S. Pat. Nos. 2,993,870, 3,206,352, 3,580,868, and 3,711,444.
Solid polyisocyanurate polymers have historically been affected by the problem of brittleness due to the high crosslink density of the trimerization network. The addition of minor amounts of polyols has been employed in the art to decrease polymer brittleness by virtue of the minor formation of polyurethane linkages. A particularly effective solution to the brittleness problem, as reflected in the improved impact strengths, for self-skinned polyisocyanurate foamed articles is disclosed in U.S. Pat. No. 3,836,424 wherein particular choices of polyol components give rise to much greater impact strengths in comparison to other polyols which do not provide the same improvements.
However, a drawback to the addition of polyols to solid polyisocyanurates is the resultant lowering which the addition causes in the high temperature resistant properties of said polyisocyanurates. Obviously, good high temperature resistance would be one of the reasons for which the polyisocyanurate would have been chosen originally for a particular application. Any lowering of this property would therefore be self-defeating.
Surprisingly, it has now been discovered that a polyol combination comprising a member from a narrow class of high molecular weight polyols with a particular diol, namely ethylene glycol, both present in particular proportions during the trimerization of an organic polyisocyanate, gives rise to solid polyisocyanurate polymers characterized by the expected good impact strength but having unexpectedly superior heat resistance compared to the corresponding polyisocyanurate polymers containing only the single polyol component of the high molecular weight class. The increased heat resistance occurs even though the latter polymers contain a lower proportion of polyurethane linkages when compared to the former.
The present polyol combinations in conjunction with organic polyisocyanates provide polyisocyanurates having unexpectedly higher heat resistance, particularly as measured by heat distortion or deflection temperatures under load measured in accordance with ASTM test procedure D-648, over what has been taught in the prior art.